A substantial number o ground contaminated areas exist, especially as the result of industrial disposal, which either threaten populated areas or which cannot be used for conventional purposes. Temporary storage methods and or/soil heating techniques have been proposed for treating contaminated soils containing dioxins, PCB'S, hydrocarbons and the like. Soil heating can drive off volatile substances but some methods of heating the soil, e.g. radio frequency heating, can be expensive or incapable of heating to the desired depth for removing large quantities of contaminants. In Brouns et al U.S. Pat. No. 4,376,598, in situ vitrification of soil is described wherein sufficient electrical energy is applied via electrodes in the ground for converting the soil itself to a conductive, i.e., liquid, state which is then allowed to harden into a vitrified mass. According to the latter method, non-volatile contaminant substances are stabilized as vitrified material, and volatile materials are driven off or pyrolyzed. However, electrical power requirements in melting the soil can be substantial.
For the purpose of carrying out complete in-situ vitrification of the soil, or in heating of the soil to temperatures for driving off contaminants, pairs of metal electrodes can be driven into the ground and connected to a source of power. Electrical discharge or current flow then tends to take place at the surface, whereby a relatively large area is liquefied or treated near ground level, but lower regions are less effectively penetrated. Lower melted soil resistance encountered near the surface during in-situ vitrification is believed to promote spreading of the treatment area adjacent the surface as compared with treatment to a greater depth. Subjecting the electrodes to high operating temperatures and corrosive environments for extended periods of time reduces electrode life. The electrodes can deteriorate rapidly as a result of emphasizing surface treatment because of oxidation as well as because of diffusion of materials into the electrodes, recrystallization of the electrode material, and/or metal reduction and pitting.